Abstract Over 40% of US young adults, ages 18-24 years, have ever tried waterpipe (WP) smoking and many users are unaware of its harmful effects and addictive potential. Health warning labels have been found to increase knowledge about the harmful effects of other tobacco products that must carry such warnings. The Food and Drug Administration (FDA) took regulatory authority over WP products in August 2016 and will require all WP tobacco sold in the US to carry a standard warning about nicotine by 2018. Our research will focus on WPs rather than WP tobacco because the majority of young adults smoke a WP in a caf and order the flavored tobacco from a menu, and thus never see the tobacco pack. Moreover, we will compare no health warning label to both a text only condition and a text/graphic condition. Little research to date has focused on graphic warning labels for WPs. The aims of our proposal are the following: 1) Determine the optimal placement of the health warning label on a WP to attract attention; 2) Using the FDA nicotine warning label, determine the effect of the presence of the text vs. text/graphic vs. no health warning label on a carbon monoxide biomarker, WP puffing, and other behaviors, including perceptions of risk as measured by the social interaction among participants during the WP smoking session; and, 3) Explore the impact of the presence of a health warning label (any label and text vs. text/graphic) on smoking behavior at 3 and 6 months post-experiment. For Aim 1, we will determine the optimal placement of heath warning labels on different WPs using focus group methods and eye tracking research. Aim 2 will measure the effect of the FDA nicotine warning label, in text-only and text/graphic formats vs. no health warning label on WP smoking behavior in a controlled laboratory setting. Participants will be recruited as dyads and randomized to text vs. text/graphic vs. no warning label. Control participants will complete two laboratory sessions and participants in the other two arms will complete three sessions, all separated by one week. Each session will be audio- and videotaped. Outcomes will include waterpipe puffing topography measures; subjective ratings of nicotine dependence, craving, and liking/disliking; exhaled carbon monoxide; and conversation topics related to fear, health risks, and the health warning label. This proposal addresses the FDA research priority area of Communications by providing the evidence needed to inform rule-making surrounding the use of effective warning labels that will correct the public misperception that WP tobacco smoking is a safe or less harmful form of tobacco use.